According to new research, published in the published in the Proceedings of the Royal Society B, Indo-Pacific bottlenose dolphins (Tursiops aduncus) living in Shark Bay, a World Heritage Site in the Gascoyne region of Western Australia, form close friendships with other dolphins that have a common interest.
Shark Bay is home to an iconic population of bottlenose dolphins, and the only place where dolphins have been observed using marine sponges as foraging tools.
This socially learned behavior, transmitted from mother to calf, helps certain dolphins (spongers) find food in deeper water channels.
While the tool-using technique is well-studied in female dolphins, the new study looked specifically at male dolphins.
Using behavioral, genetic and photographic data collected from 124 male dolphins during the winter months in Shark Bay over nine years (2007-2015), University of Zurich researcher Manuela Bizzozzero and colleagues analyzed a subset of 37 male dolphins, comprising 13 spongers and 24 non-spongers.
Male spongers spend more time associating with other male spongers than they do non-spongers, these bonds being based on similar foraging techniques and not relatedness or other factors.
“Male dolphins in Shark Bay exhibit a fascinating social system of nested alliance formation,” Dr. Bizzozzero said.
“These strong bonds between males can last for decades and are critical to each male’s mating success.”
“We were very excited to discover alliances of spongers, dolphins forming close friendships with others with similar traits.”
“Foraging with a sponge is a time-consuming and largely solitary activity so it was long thought incompatible with the needs of male dolphins in Shark Bay — to invest time in forming close alliances with other males,” said Dr. Simon Allen, a researcher at the Universities of Bristol.
“This study suggests that, like their female counterparts and indeed like humans, male dolphins form social bonds based on shared interests.”
M.R. Bizzozzero et al. 2019. Tool use and social homophily among male bottlenose dolphins. Proc. R. Soc. B 286 (1904): 20190898; doi: 10.1098/rspb.2019.0898